The subject matter disclosed herein relates to an optical sensor used in a safety system and, more specifically, to a system to test performance of the optical receiver used in the optical sensor.
An optical sensor includes a receiver that converts light incident to the sensor into an electric signal. The receiver may include a single photosensitive device or an array of pixels, for example charge-coupled devices (CCD) or complementary metal-oxide-semiconductor (CMOS) sensors. Each pixel converts the light incident to that pixel to a separate electrical signal. The optical sensor typically has an opening through which the light passes and may further include a lens or optical filter over the opening to focus the light on the detector. Depending on the application requirements and the configuration of the sensor, the optical sensor is suited for a variety of uses ranging from indicating the presence of a beam of light to reproducing a three dimensional (3D) image of an object.
It is known that the sensitivity of the receivers changes over time. Although variation in the rate of change for individual pixels naturally occurs, on average the performance of the pixel array will change at a generally uniform rate. By sampling the performance of a portion of the pixel array, the condition of the entire array may be monitored without being susceptible to variations from individual pixels. The performance of the detector may be tested by directing a reference light source toward a portion of the pixel array to be tested and measuring the resulting electrical signals. Comparing the resulting electrical signals to an expected value can be used to detect changes in the performance of the sensor.
However, optical sensors are often used in applications that are not conducive to supplying a reference light for testing of the sensor. For example, the sensor may be a component of a safety system such as a light curtain or a 3D camera monitoring access to or operation of an industrial machine or process line. The machine or process line may operate on a near-continuous basis with periodic maintenance scheduled on a monthly or even less frequent interval. Because the safety system is typically protecting an operator from a potentially hazardous operating region or condition, industrial standards require more frequent monitoring of the operating performance than achieved by periodic maintenance alone.
Thus, it would be desirable to provide a system that regularly tests operation of the sensor without interrupting normal operation of the sensor.